Single-cell RNA sequencing reveals the regenerative potential of thyroid follicular epithelial cells in metastatic thyroid carcinoma

Thyroid stimulating hormone deficiency is the cornerstone of treatment for metastatic thyroid cancer. Due to the loss of follicular epithelial cells in thyroid cancer, the thyroid gland degenerates to 85% of its original size. When thyroid stimulating hormone is restored, follicular epithelial cells in thyroid cancer regenerate, which is postulated to be related to stem-like cells. By single cell RNA seq, we found a group of rare thyroid follicular epithelial cells in mouse metastatic thyroid cancer, which expressed stem-like genes (CD44V6⁺ and CD133⁺) and a large number of differentiated cells (CD44V6⁺ and CD24⁺). In mouse and in organoids, the two subsets contribute equally to metastatic thyroid cancer regeneration. The analysis of human metastatic thyroid cancer revealed that the differentiated thyroid follicular epithelial cell subpopulation was similar to that of the stem like epithelial cell subpopulation, and the regeneration potential was also enhanced after thyroid stimulating hormone ablation. Accordingly, we propose that the regeneration of metastatic thyroid cancer is driven by almost all persistent thyroid follicular epithelial cells, not only by few stem-like cells.

Heregulin controls ERα and HER2 signaling in mammospheres of ERα-positive breast cancer cells and interferes with the efficacy of molecular targeted therapy

Estrogen receptor (ER)α and the human epidermal growth factor receptor (HER) family are inversely expressed in ERα-positive cancer in association with resistance to hormonal therapy, but the mechanism underlying their relationship remains unknown. We analyzed the effect of HER family ligands on the expression of ER and the HER family in ERα-positive MCF-7 and T47D breast cancer cell lines in 3D spheroid culture. Here, we demonstrated for the first time that heregulin-1β (HRG), a HER3 and HER4 ligand, most effectively regulated ER/HER family expression by decreasing ERα mRNA expression and increasing HER family mRNA expression. HRG treatment attenuated fulvestrant-mediated growth inhibition, and promoted the migration of MCF-7 cells. Moreover, HRG increased the CD44⁺/CD24^- cell fraction and side population cells, both of which are recognized as prospective breast cancer stem cell markers. HRG activated both phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) and mitogen-activated protein kinase (MAPK) pathways. Inhibitors of these pathways reduced the growth of MCF-7 cells, but the addition of HRG has different effects on these pathways. HRG blocked the inhibitory effect of mTOR inhibitors, such as rapamycin and everolimus, on cell growth but not that of a PI3K inhibitor. Furthermore, HRG slightly decreased the inhibitory effect of an AKT inhibitor on cell growth. In contrast, HRG enhanced the MEK inhibitor-induced inhibition of cell growth. These findings suggest that HRG-stimulated signaling pathways allow ERα-positive breast cancer cells to escape from growth inhibition caused by everolimus, via MAPK signaling and/or other signaling pathways. Everolimus improves progression-free survival in combination with exemestane as second-line therapy for metastatic hormone receptor-positive breast cancer. Our study suggests that HRG is a novel target for ERα-positive breast cancer therapy.

A novel miR-200c/c-myc negative regulatory feedback loop is essential to the EMT process, CSC biology and drug sensitivity in nasopharyngeal cancer

Overexpression of the c-Myc oncogene has been implicated in cancer stem cell - like (CSC) phenotypes and epithelial-to-mesenchymal transition (EMT) in cancer. However, the underlying molecular mechanism by which c-Myc regulates EMT and CSC potential in remains unclear. In the present study, we showed that the expression of c-Myc protein is inversely correlated with microRNA (miR)-200c expression in primary tumor samples from nasopharyngeal cancer (NPC) patients. We further demonstrated that Myc and miR-200c negatively regulate the expression each other in NPC cell lines. c-Myc transcriptionally repressed expression of miR-200c by directly binding to two E-box sites located within a 1 kb segment upstream of TSS of the miR-200c. In addition, miR-200c post-transcriptionally repressed expression of c-Myc by binding to its 3'-untranslated region, suggesting the existence of a negative feedback loop between Myc and miR-200c. Overexpression of c-Myc interfered with this feedback loop and activated the EMT program, induced CSC phenotypes, and enhanced drug sensitivity, whereas miR-200c could counteract these biological effects of c-Myc. Our results provide a novel mechanism governing c-Myc and miR-200c expression and indicate that either targeting c-Myc or restoring miR-200c expression would be a promising approach to overcome oncogenic role of c-Myc in NPC.

Verification of EZH2 as a druggable target in metastatic uveal melanoma

BACKGROUND

Hepatic metastasis develops in ~ 50% of uveal melanoma (UM) patients with no effective treatments. Although GNAQ/GNA11 mutations are believed to confer pathogenesis of UM, the underlying mechanism of liver metastasis remains poorly understood. Given that profound epigenetic evolution may occur in the long journey of circulating tumor cells (CTCs) to distant organs, we hypothesized that EZH2 endowed tumor cells with enhanced malignant features (e.g., stemness and motility) during hepatic metastasis in UM. We aimed to test this hypothesis and explore whether EZH2 was a therapeutic target for hepatic metastatic UM patients.

METHODS

Expression of EZH2 in UM was detected by qRT-PCR, Western blotting and immunohistochemistry staining. Proliferation, apoptosis, cancer stem-like cells (CSCs) properties, migration and invasion were evaluated under circumstances of treatment with either EZH2 shRNA or EZH2 inhibitor GSK126. Antitumor activity and frequency of CSCs were determined by xenografted and PDX models with NOD/SCID mice. Hepatic metastasis was evaluated with NOG mice.

RESULTS

We found that EZH2 overexpressed in UM promoted the growth of UM; EZH2 increased the percentage and self-renewal of CSCs by miR-29c-DVL2-β-catenin signaling; EZH2 facilitates migration and invasion of UM cells via RhoGDIγ-Rac1 axis. Targeting EZH2 either by genetics or small molecule inhibitor GSK126 decreased CSCs and motility and abrogated the liver metastasis of UM.

CONCLUSIONS

These findings validate EZH2 as a druggable target in metastatic UM patients, and may shed light on the understanding and interfering the complicated metastatic process.

In Vitro Employment of Recombinant Taenia solium Calreticulin as a Novel Strategy Against Breast and Ovarian Cancer Stem-like Cells

BACKGROUND AND AIMS

Calreticulin is a chaperone and master regulator of intracellular calcium homeostasis. Several additional functions have been discovered. Human and parasite calreticulin have been shown to suppress mammary tumor growth in vivo. Here, we explored the capacity of recombinant Taenia solium calreticulin (rTsCRT) to modulate cancer cell growth in vitro.

METHODS

We used different concentrations of rTsCRT to treat cancer cell lines and analyzed viability and colony formation capacity. We also tested the combination of the IC₂₀ or IC₅₀ doses of rTsCRT and of the chemotherapeutic drug 5-fluorouracil on MCF7 and SKOV3 cell lines. As a control, the non-tumorigenic cell line MCF10-A was employed. The effect of the drug combinations was also assessed in cancer stem-like cells. Additionally, scavenger receptor ligands were employed to identify the role of this receptor in the rTsCRT anti-tumoral effect.

RESULTS

rTsCRT has a dose-dependent in vitro anti-tumoral effect, being SKOV3 the most sensitive cell line followed by MCF7. When rTsCRT/5-fluorouracil were used, MCF7 and SKOV3 showed a 60% reduction in cell viability; colony formation capacity was also diminished. Treatment of cancer stem-like cells from MCF7 showed a higher reduction in cell viability, while those from SKOV3 were more sensitive to colony disaggregation. Finally, pharmacological inhibition of the scavenger receptor, abrogated the reduction in viability induced by rTsCRT in both the parental and stem-like cells.

CONCLUSION

Our data suggest that rTsCRT alone or in combination with 5-fluorouracil inhibits the growth of breast and ovarian cancer cell lines through its interaction with scavenger receptors.

Salinomycin effectively eliminates cancer stem-like cells and obviates hepatic metastasis in uveal melanoma

BACKGROUND

Uveal melanoma (UM) is the most common primary intraocular tumor. Hepatic metastasis is the major and direct death-related reason in UM patients. Given that cancer stem-like cells (CSCs) are roots of metastasis, targeting CSCs may be a promising strategy to overcome hepatic metastasis in UM. Salinomycin, which has been identified as a selective inhibitor of CSCs in multiple types of cancer, may be an attractive agent against CSCs thereby restrain hepatic metastasis in UM. The objective of the study is to explore the antitumor activity of salinomycin against UM and clarify its underlying mechanism.

METHODS

UM cells were treated with salinomycin, and its effects on cell proliferation, apoptosis, migration, invasion, CSCs population, and the related signal transduction pathways were determined. The in vivo antitumor activity of salinomycin was evaluated in the NOD/SCID UM xenograft model and intrasplenic transplantation liver metastasis mouse model.

RESULTS

We found that salinomycin remarkably obviated growth and survival in UM cell lines and in a UM xenograft mouse model. Meanwhile, salinomycin significantly eliminated CSCs and efficiently hampered hepatic metastasis in UM liver metastasis mouse model. Mechanistically, Twist1 was fundamental for the salinomycin-enabled CSCs elimination and migration/invasion blockage in UM cells.

CONCLUSIONS

Our findings suggest that targeting UM CSCs by salinomycin is a promising therapeutic strategy to hamper hepatic metastasis in UM. These results provide the first pre-clinical evidence for further testing of salinomycin for its antitumor efficacy in UM patients with hepatic metastasis.

Plumbagin inhibits cancer stem-like cells, angiogenesis and suppresses cell proliferation and invasion by targeting Wnt/β-catenin pathway in endocrine resistant breast cancer

Fifty percent of advanced stage ER-positive breast cancer patients develop endocrine resistance. Aberrant activation of Wnt/β-catenin is associated with stem-like phenotypes and epithelial-mesenchymal transition (EMT) process which confers resistance to endocrine therapy. Cancer stem-like cells (CSLCs) can be a vital source of proangiogenic factors including fibroblast growth factor 2 (FGF2) which drives angiogenesis and leads to tumor growth and metastasis. Therefore, targeting Wnt and FGF2 may provide effective treatment for endocrine resistant breast cancer. Our previous in vitro study reported that plumbagin (PLB) was a potent anticancer agent and was able to inhibit EMT in endocrine-resistant cells. This study aimed to further investigate the inhibitory effects of PLB on cancer stem-like phenotypes, tumorigenicity and angiogenesis. The results demonstrated Wnt/β-catenin signaling was activated and was able to form mammospheres with increased cancer stem cell markers (ALDH1, NANOG, and OCT4) in endocrine-resistant cells. PLB significantly inhibited colony-forming, mammosphere formation and decreased cancer stem cell markers. The inhibitory effects of PLB on cell proliferation and invasion were mediated by Wnt signaling pathway. PLB also significantly reduced Wnt responsive genes and β-catenin. Moreover, PLB treatment at doses of 2 and 4 mg/kg/day inhibited tumor growth, angiogenesis and metastasis without any adverse effects on body weight and blood coagulation in orthotopic xenograft nude mice. In conclusion, PLB exerted anti-cancer activity and eliminated stem-like properties by attenuating Wnt/β-catenin signaling and FGF2 expression. These findings suggest that PLB could be a promising agent to treat endocrine resistant breast cancer.

Transcriptional inhibition by CDK7/9 inhibitor SNS-032 abrogates oncogene addiction and reduces liver metastasis in uveal melanoma

Background

Life of patients with uveal melanoma (UM) is largely threatened by liver metastasis. Little is known about the drivers of liver organotropic metastasis in UM. The elevated activity of transcription of oncogenes is presumably to drive aspects of tumors. We hypothesized that inhibition of transcription by cyclin-dependent kinase 7/9 (CDK7/9) inhibitor SNS-032 diminished liver metastasis by abrogating the putative oncogenes in charge of colonization, stemness, cell motility of UM cells in host liver microenvironment.

Methods

The effects of SNS-032 on the expression of the relevant oncogenes were examined by qRT-PCR and Western blotting analysis. Proliferative activity, frequency of CSCs and liver metastasis were evaluated by using NOD-SCID mouse xenograft model and NOG mouse model, respectively.

Results

The results showed that CDK7/9 were highly expressed in UM cells, and SNS-032 significantly suppressed the cellular proliferation, induced apoptosis, and inhibited the outgrowth of xenografted UM cells and PDX tumors in NOD-SCID mice, repressed the cancer stem-like cell (CSC) properties through transcriptional inhibition of stemness-related protein Krüppel-like factor 4 (KLF4), inhibited the invasive phonotypes of UM cells through matrix metalloproteinase 9 (MMP9). Mechanistically, SNS-032 repressed the c-Myc-dependent transcription of RhoA gene, and thereby lowered the RhoA GTPase activity and actin polymerization, and subsequently inhibited cell motility and liver metastasis.

Conclusions

In conclusion, we validate a set of transcription factors which confer metastatic traits (e.g., KLF4 for CSCs, c-Myc for cell motility) in UM cells. Our results identify SNS-032 as a promising therapeutic agent, and warrant a clinical trial in patients with metastatic UM.

The Heterogeneity of Osteosarcoma: The Role Played by Cancer Stem Cells

Osteosarcoma is the most common bone sarcoma and is one of the cancer entities characterized by the highest level of heterogeneity in humans. This heterogeneity takes place not only at the macroscopic and microscopic levels, with heterogeneous micro-environmental components, but also at the genomic, transcriptomic and epigenetic levels. Recent investigations have revealed the existence in osteosarcoma of cancer cells with stemness properties. Cancer stem cells are characterized by their specific phenotype and low cycling capacity, and are linked to drug resistance, tumour growth and the metastatic process. In addition, cancer stem cells contribute to the enrichment of tumour heterogeneity. The present manuscript will describe the main characteristic features of cancer stem cells in osteosarcoma and will discuss their impact on maintaining tumour heterogeneity. Their clinical implications will also be briefly addressed.

Targeting Mcl-1 inhibits survival and self-renewal of hepatocellular cancer stem-like cells

Myeloid cell leukemia-1 (Mcl-1) is highly expressed in tumor tissues and cells of hepatocellular carcinoma (HCC), yet the role of Mcl-1 in cancer stem-like cells (CSLCs) remains largely unclear. Herein, we showed that knockdown of Mcl-1 significantly inhibited HCC cells to form spheres under ultra-low attachment condition in serum-free medium, and also attenuated clone formation. Inhibition of Mcl-1 by specific inhibitors S63845 or A-1210477 hindered secondary sphere formation, triggered apoptosis signaling and reduced the level of stem cell transcription factor Nanog, Sox2 and KLF4 in HCC spheroids cells. This study suggests that Mcl-1 is an essential factor for the survival and self-renewal of HCC CSLCs.

The rBC2LCN-positive subpopulation of PC-3 cells exhibits cancer stem-like properties

The recombinant lectin rBC2LCN is a useful marker for discriminating the undifferentiated status of human induced or embryonic stem cells. Recently, rBC2LCN has also been used for detecting some cancers and niche cells. However, the generality of which types of cells are detected by rBC2LCN is unclear. In this study, we demonstrated the potential of rBC2LCN as a probe for detecting and isolating cancer stem-like cells. Interestingly, flow cytometric analysis of various human cell lines indicated that the human prostate cancer cell line PC-3 consisted of rBC2LCN-positive and -negative subpopulations. Compared with the rBC2LCN-negative subpopulation, the rBC2LCN-positive subpopulation possessed representative features of cancer stem cells and malignancy, such as slow proliferation, increased cell motility, anchorage-independent growth, and drug resistance. The comprehensive expression profiles revealed that the rBC2LCN-positive subpopulation expressed higher levels of cancer stem cell markers. These findings indicate that rBC2LCN is useful for detecting not only pluripotent stem cells but also the cancer stem-like subpopulation of PC-3 cells. Pluripotent and cancer cells with rBC2LCN positivity would be important for future stem cell research.

Role of OCT4 in cancer stem-like cells and chemotherapy resistance

Cancer stem-like cells (CSCs) contribute to the tumorigenicity, progression, and chemoresistance of cancers. It is not known whether CSCs arise from normal stem cells or if they arise from differentiated cancer cells by acquiring self-renewal features. These CSCs share stem cell markers that normal stem cells express. There is a rising interest in octamer-binding transcription factor 4 (OCT4), one of the stem cell factors that are essential in embryogenesis and pluripotency. OCT4 is also overexpressed in CSCs of various cancers. Although the majority of the studies in CSCs reported a positive association between the expression of OCT4 and chemoresistance and an inverse correlation between OCT4 and clinical prognosis, there are studies rebuking these findings, possibly due to the sparsity of stem cells within tumors and the heterogeneity of tumors. In addition, post-translational modification of OCT4 affects its activity and warrants further investigation for its association with chemoresistance and prognosis.

Kinetic modeling of tumor regression incorporating the concept of cancer stem-like cells for patients with locally advanced lung cancer

Background

Personalized medicine for patients receiving radiation therapy remains an elusive goal due, in part, to the limits in our understanding of the underlying mechanisms governing tumor response to radiation. The purpose of this study was to develop a kinetic model, in the context of locally advanced lung cancer, connecting cancer cell subpopulations with tumor volumes measured during the course of radiation treatment for understanding treatment outcome for individual patients.

Methods

The kinetic model consists of three cell compartments: cancer stem-like cells (CSCs), non-stem tumor cells (TCs) and dead cells (DCs). A set of ordinary differential equations were developed to describe the time evolution of each compartment, and the analytic solution of these equations was iterated to be aligned with the day-to-day tumor volume changes during the course of radiation treatment. A least squares fitting method was used to estimate the parameters of the model that include the proportion of CSCs and their radio-sensitivities. This model was applied to five patients with stage III lung cancer, and tumor volumes were measured from 33 cone-beam computed tomography (CBCT) images for each of these patients. The analytical solution of these differential equations was compared with numerically simulated results.

Results

For the five patients with late stage lung cancer, the derived proportions of CSCs are 0.3 on average, the average probability of the symmetry division is 0.057 and the average surviving fractions of CSCs is 0.967, respectively. The derived parameters are comparable to the results from literature and our experiments. The preliminary results suggest that the CSC self-renewal rate is relatively small, compared to the proportion of CSCs for locally advanced lung cancers.

Conclusions

A novel mathematical model has been developed to connect the population of cancer stem-like cells with tumor volumes measured from a sequence of CBCT images. This model may help improve our understanding of tumor response to radiation therapy, and is valuable for development of new treatment regimens for patients with locally advanced lung cancer.

Development of a novel and economical agar-based non-adherent three-dimensional culture method for enrichment of cancer stem-like cells

BACKGROUND

Non-adherent or ultra-low attachment three-dimensional (3D) culture, also called sphere formation assay, has been widely used to assess the malignant phenotype and stemness potential of transformed or cancer cells. This method is also popularly used to isolate the cancer stem-like cells (CSCs) or tumor-initiating cells based on their unique anchorage-independent growth or anoikis-resistant capacity. Different non-adhesive coating agents, such as poly-2-hydroxyethyl methacrylate (poly-HEMA) and synthetic hydrogels, have been used in this non-adherent 3D culture. However, preparation of non-adherent culture-ware is labor-intensive and technically demanding, and also costs of commercial non-adherent culture-ware prepared with various coating agents are relatively expensive and the culture-ware cannot be used repeatedly.

METHODS

In this study, we developed a non-adherent 3D culture method based on agar coating for growing tumor spheres derived from various cancer cell lines and primary prostate cancer tissues under a non-adherent and serum-free condition. The tumor spheres generated by this 3D culture method were analyzed on their expression profiles of CSC-associated markers by reverse transcription quantitative polymerase chain reaction, presence and relative proportion of CSCs by fluorescence-activated cell sorting (CD133⁺/CD44⁺ cell sorting) and also a CSC-visualizing reporter system responsive to OCT4 and SOX2 (SORE6), and in vivo tumorigenicity. The repeated use of agar-coated plates for serial passages of tumor spheres was also evaluated.

RESULTS

Our results validated that the multicellular tumor spheres generated by this culture method were enriched of CSCs, as evidenced by their enhanced expression profiles of CSC markers, presence of CD133⁺/CD44⁺ or SORE6⁺ cells, enhanced self-renewal capacity, and in vivo tumorigenicity, indicating its usefulness in isolation and enrichment of CSCs. The agar-coated plates could be used multiple times in serial passages of tumor spheres.

CONCLUSIONS

The described agar-based 3D culture method offers several advantages as compared with other methods in isolation of CSCs, including its simplicity and low-cost and repeated use of agar-coated plates for continuous passages of CSC-enriched spheres.

Cancer cell plasticity: Impact on tumor progression and therapy response

Most tumors exhibit intra-tumor heterogeneity, which is associated with disease progression and an impaired response to therapy. Cancer cell plasticity has been proposed as being an important mechanism that, along with genetic and epigenetic alterations, promotes cancer cell diversity and contributes to intra-tumor heterogeneity. Plasticity endows cancer cells with the capacity to shift dynamically between a differentiated state, with limited tumorigenic potential, and an undifferentiated or cancer stem-like cell (CSC) state, which is responsible for long-term tumor growth. In addition, it confers the ability to transit into distinct CSC states with different competence to invade, disseminate and seed metastasis. Cancer cell plasticity has been linked to the epithelial-to-mesenchymal transition program and relies not only on cell-autonomous mechanisms, but also on signals provided by the tumor microenvironment and/or induced in response to therapy. We provide an overview of the dynamic transition for cancer cell states, the mechanisms governing cell plasticity and their impact on tumor progression, metastasis and therapy response. Understanding the mechanisms involved in cancer cell plasticity will provide insights for establishing new therapeutic interventions.

Regorafenib suppresses colon tumorigenesis and the generation of drug resistant cancer stem-like cells via modulation of miR-34a associated signaling

Background

Colorectal cancer (CRC) is one of the most prevalent malignancies in the world and developed drug resistance has represented one of the most challenging tasks for management. The current therapeutic regimens may select and enrich cancer stem-like cells (CSCs) resulting in the increased resistance against treatment, metastatic potential and mortality. Regorafenib is a multi-kinase inhibitor, an FDA-approved last-of-line treatment for patients with chemo-refractory metastatic CRC. However, regorafenib’s potential effects on CSCs have not been fully elucidated.

Methods

Here, we developed two 5-FU resistant CRC cell lines, HCT-116R and DLD-1R and showed the increased CSCs characteristics such as increased side-population cells, tumor sphere formation and expression of stemness markers. These cell lines and CSCs properties were used for evaluating the potential of regorafenib in suppressing CSCs.

Results

We showed that regorafenib treatment decreased the stemness phenotypes including tumor sphere formation, and side-population, of both HCT-116R and DLD-1R cells. Additionally, regorafenib suppressed the cell viability in both cell lines synergistically with 5-FU. In vivo, the combination of regorafenib and 5-FU significantly suppressed the tumorigenesis and stemness markers of 5-FU resistant DLD-1R. Mechanistically, regorafenib-mediated effects were associated with the induction of tumor suppressor miR-34a and suppression of WNT/β-catenin signaling. Our findings demonstrated that regorafenib treatment was associated with the increased level of miR-34a, resulting in reversing drug resistance and cancer-initiating cell phenotypes by degrading WNT/β-catenin in CRC.

Conclusion

Regorafenib might be a potential drug for colon cancer stem-like cells and it should be investigated in future clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0836-x) contains supplementary material, which is available to authorized users.

On reprogramming of tumor cells metabolism: detection of glycogen in the cell lines of hepatocellular origin with various degrees of dedifferentiation

The reprogramming of cancer cells includes shifts in glucose and glycogen metabolism. The aim of our work was to check the ability of forming glycogen grains in hepatocellular tumor cell lines of various dedifferentiation levels. We studied the monolayer culture established in vitro after explanting cells from rat ascites Zajdela hepatoma strain C (ZH-C) as a "parental" line and its five daughter clonal sublines: the holoclonal sublines 3H, 5F, 6H and the meroclonal ones 1E, 9C, which possess, respectively, the properties of cancer stem-like cells (CSLCs) and cancer progenitor-like cells (CPLCs). Besides, we studied four permanent cell lines of a rat hepatoma HTC, two murine hepatomas BWTG3 and MH-22a, and human hepatoblastoma HepG2. We used normal rat hepatocytes as positive control cells that form glycogen. We estimated relative cell dedifferentiation levels of the studied lines via analysis of cell morphology, morphometry and motility character on stained cell preparations and lifetime video files. Glycogen in the cells was detected using a Schiff type Au-SO2 reagent. All studied hepatocellular tumor lines were not of equal dedifferentiation level as manifested by different nucleus-to-cytoplasm ratio, by epithelium-like or fibroblast-like morphology, by tight or loosen intercellular contacts, by cell migration of collective or individual types. Glycogen fluorescence of uneven intensity was observed in all normal rat hepatocytes, but only in some cell groups or in single cells of hepatocellular tumor lines. The large or small fluorescent grains were found not only in relatively less dedifferentiated parental ZH-C line, BWTG3 and HepG2 lines, but also in moderately dedifferentiated 1E and HTC lines and even in severely dedifferentiated 3H, 5F and 6H sublines, as well as in the islets of the rat ascites hepatoma induced in vivo by the injection of 3H cells (the tumor-initiating cells). On the other hand, MH-22 and 9C lines, being relatively less and moderately dedifferentiated, showed no glycogen fluorescence. Thus, in 10 tumor cell lines of hepatocellular origin, an ability to reserve glycogen manifested no obvious dependency on their dedifferentiation level. Glycogen grains were detected in some cells even of the severely dedifferentiated lines: in single CSLCs of holoclonal ZH sublines grown in vitro and in a majority of tumor-initiating cells derived from ascites hepatoma in vivo. We suggest that dynamic changes in glycogen formation in CSLCs and tumor-initiating cells might be of importance for their dedifferentiation, self-renewal in vitro, survival and metastasis in vivo. The role of glycogen in maintaining viability and metastasis of tumor cells is to be further studied.

Long Non-coding RNA Linc-ROR Is Upregulated in Papillary Thyroid Carcinoma

Long non-coding RNAs (lncRNAs) may contribute to carcinogenesis and tumor progression by regulating transcription and gene expression. The role of lncRNAs in the regulation of thyroid cancer progression is being extensively examined. Here, we analyzed three lncRNAs that were overexpressed in papillary thyroid carcinomas, long intergenic non-protein coding RNA, regulator of reprogramming (Linc-ROR, ROR) PVT1 oncogene (PVT1), and HOX transcript antisense intergenic RNA (HOTAIR) to determine their roles in thyroid tumor development and progression. ROR expression has not been previously examined in thyroid carcinomas. Tissue microarrays (TMAs) of formalin-fixed paraffin-embedded tissue sections from 129 thyroid cases of benign and malignant tissues were analyzed by in situ hybridization (ISH), automated image analysis, and real-time PCR. All three lncRNAs were most highly expressed in the nuclei of PTCs. SiRNA experiments with a PTC cell line, TPC1, showed inhibition of proliferation with siRNAs for all three lncRNAs while invasion was inhibited with siRNAs for ROR and HOTAIR. SiRNA experiments with ROR also led to increased expression of miR-145, supporting the role of ROR as an endogenous miR-145 sponge. After treatment with TGF-β, there was increased expression of ROR, PVT1, and HOTAIR in the PTC1 cell line compared to control groups, indicating an induction of their expression during epithelial to mesenchymal transition (EMT). These results indicate that ROR, PVT1, and HOTAIR have important regulatory roles during the development of PTCs.

Hypericin affects cancer side populations via competitive inhibition of BCRP

OBJECTIVE

Cancer stem-like cells (CSLCs) are considered a root of tumorigenicity and resistance. However, their identification remains challenging. The use of the side population (SP) assay as a credible marker of CSLCs remains controversial. The SP assay relies on the elevated activity of ABC transporters that, in turn, can be modulated by hypericin (HYP), a photosensitizer and bioactive compound of St. John's Wort (Hypericum perforatum), a popular over-the-counter antidepressant. Here we aimed to comprehensively characterize the SP phenotype of cancer cells and to determine the impact of HYP on these cells.

METHODS

Flow cytometry and sorting-based assays were employed, including CD24-, CD44-, CD133-, and ALDH-positivity, clonogenicity, 3D-forming ability, ABC transporter expression and activity, and intracellular accumulation of HYP/Hoechst 33342. The tumorigenic ability of SP, nonSP, and HYP-treated cells was verified by xenotransplantation into immunodeficient mice.

RESULTS

The SP phenotype was associated with elevated expression of several investigated transporters and more intensive growth in non-adherent conditions but not with higher clonogenicity, tumorigenicity or ALDH-positivity. Despite stimulated BCRP level and MRP1 activity, HYP reversibly decreased the SP proportion, presumably via competitive inhibition of BCRP. HYP-selected SP cells acquired additional traits of resistance and extensively eliminated HYP.

CONCLUSIONS

Our results suggest that SP is not an unequivocal CSLC-marker. However, SP could play an important role in modulating HYP-treatment and serve as a negative predictive tool for HYP-based therapies. Moreover, the use of supplements containing HYP by cancer patients should be carefully considered, due to its proposed effect on drug efflux and complex impact on tumor cells, which have not yet been sufficiently characterized.

Identification of antigenic peptides from novel renal cancer stem-like cell antigen, DNAJB8

OBJECTIVES

To identify antigenic peptides of cancer stem-like cells (CSCs) antigen, DNAJB8, and establish a mouse CSCs-targeting immunotherapy model.

MATERIALS AND METHODS

To induce DNAJB8-specific immune reaction, we stimulated human CD8⁺ lymphocytes with antigen-presenting cells pulsed with a cocktail of three candidate HLA-A*24:02 restricted peptides and assessed peptide specific human cytotoxic T lymphocytes (CTLs) induction. One of the antigenic peptides showed identical amino acid sequence as corresponding mouse DNAJB8. We evaluated CTL induction with the peptide immunization in mouse model.

RESULTS

We confirmed peptide-specific interferon-γ secretions and cytotoxic activities of induced human CTLs. In vivo immunization with the peptide to mice, peptide-specific CTL response could be observed in mouse CD8⁺ T cells. Furthermore, immunization with the peptide showed significant anti-tumor effects compared with negative controls.

CONCLUSION

DNAJB8-derived peptide is a novel candidate for CSCs-targeting immunotherapy, and mouse models can be used to evaluate CSCs-targeting immunotherapy.

Tumor cell-associated immune checkpoint molecules - Drivers of malignancy and stemness

Inhibitory or stimulatory immune checkpoint molecules are expressed on a sizeable fraction of tumor cells in different tumor types. It was thought that the main function of tumor cell-associated immune checkpoint molecules would be the modulation (down- or upregulation) of antitumor immune responses. In recent years, however, it has become clear that the expression of immune checkpoint molecules on tumor cells has important consequences on the biology of the tumor cells themselves. In particular, a causal relationship between the expression of these molecules and the acquisition of malignant traits has been demonstrated. Thus, immune checkpoint molecules have been shown to promote the epithelial-mesenchymal transition of tumor cells, the acquisition of tumor-initiating potential and resistance to apoptosis and antitumor drugs, as well as the propensity to disseminate and metastasize. Herein, we review this evidence, with a main focus on PD-L1, the most intensively investigated tumor cell-associated immune checkpoint molecule and for which most information is available. Then, we discuss more concisely other tumor cell-associated immune checkpoint molecules that have also been shown to induce the acquisition of malignant traits, such as PD-1, B7-H3, B7-H4, Tim-3, CD70, CD28, CD137, CD40 and CD47. Open questions in this field as well as some therapeutic approaches that can be derived from this knowledge, are also addressed.

Effective treatment of drug resistant recurrent breast tumors harboring cancer stem-like cells by staurosporine/epirubicin co-loaded polymeric micelles

Breast cancer recurrence and resistance are associated with cancer stem-like cell (CSC) sub-populations. As conventional therapies fail to treat CSCs, institution of novel therapeutic strategies capable of eradicating both cancer cells and CSCs is central for achieving effective treatments with long-term survival. Here, we studied the ability of polymeric micelles cooperatively loading the cytotoxic drug epirubicin (Epi) and the CSC inhibitor staurosporine (STS) to treat breast tumors, particularly when tumors relapsed after chemotherapy. The STS/Epi-loaded micelles (STS/Epi/m) demonstrated potent therapeutic efficacy against both naïve orthotopic 4T1-luc breast tumors and their recurrent Epi-resistant counterparts, significantly prolonging survival. This efficacy enhancement of STS/Epi/m was correlated with the ability of the micelles to suppress the CSC-associated sub-populations of breast cancer, i.e. the aldehyde dehydrogenase-positive (ALDH⁺) population and the CD44⁺/CD24^- fraction, in Epi-resistant cells and tumors. These results demonstrated STS/Epi/m as a promising strategy for effective management of breast cancer.

Near infrared light triggered nitric oxide releasing platform based on upconversion nanoparticles for synergistic therapy of cancer stem-like cells

Near infrared (NIR) light-driven nitric oxide (NO) release nano-platform based on upconversion nanoparticles (UCNPs) and light sensitive NO precursor Roussin's black salt (RBS) was fabricated to generate NO upon 808nm irradiation. The application of 808nm laser as the excitation source could achieve better penetration depth and avoid overheating problem. The combination of UCNPs and RBS could realize the on-demand release of NO at desired time and location by simply controlling the output of NIR laser. Cellular uptake results showed that more nanoparticles were internalized in cancer stem-like cells (CSCs) rather than non-CSCs. Therefore, a synergistic cancer therapy strategy to eradicate both CSCs and non-CSCs simultaneously was developed. Traditional chemo-drug could inhibit non-CSCs but has low killing efficiency in CSCs. However, we found that the combination of NO and chemotherapy could efficiently inhibit CSCs in bulk cells, including inhibiting mammosphere formation ability, decreasing CD44⁺/CD24^- subpopulation and reducing tumorigenic ability. The mechanism studies confirmed that NO could not only induce apoptosis but also increase drug sensitivity by declining drug efflux in CSCs. This UCNPs-based platform may provide a new combinatorial strategy of NO and chemotherapy to improve cancer treatment.

Cripto-1 acts as a functional marker of cancer stem-like cells and predicts prognosis of the patients in esophageal squamous cell carcinoma

Background

Esophageal squamous cell carcinoma (ESCC) is highly malignant with highly invasive and metastatic capabilities and poor prognosis. It is believed that the ESCC cancer stem-like cells (ECSLCs) are critical for tumorigenicity, invasion and metastasis of ESCC. However, the properties of ECSLCs vary with different markers used in isolation, so that new and more effective markers of ECSLCs need to be identified. This study aimed to estimate the potentiality of Cripto-1 (CR-1) as an ECSLC surface marker and investigate the clinical significance of CR-1 expression in ESCC.

Methods

ESCC cells with CR-1 ^high or CR-1^low were obtained by flow cytometry then their self-renewal capability and tumorigenicity were compared by colony and limiting dilution sphere formation analysis in vitro and xenograft in nude mice in vivo, respectively. Knockdown of CR-1 expression in ESCC cells was conducted with short hairpin RNA. Cell migration and invasion were examined by scratch test and matrigel transwell assay, respectively. Metastatic capability of ESCC cells was assayed by a mouse tail vein metastasis model. The levels of CR-1 expression in cancerous and paired adjacent normal tissues were assessed by IHC and qRT-RCR.

Results

CR-1^high subpopulation of ESCC cells isolated by FACS expressed high level of genes related to stemness and epithelial-mesenchymal transition (EMT), and possessed high capacities of self-renewal, tumorigenesis, invasion and metastasis. Suppression of CR-1 expression significantly reduced the expression of stemness- and EMT-related genes and the capabilities of self-renewal in vitro, tumorigenicity and metastasis in vivo in ESCC cells. In the clinical ESCC specimens, the expression levels of CR-1 in cancerous tissues were positively correlated to TNM stage, invasive depth, and lymph node metastasis. Cox regression analysis indicated that CR-1 was an independent indicator of prognosis. The expression of CR-1 was found overlapping with aldehyde dehydrogenase 1A1 (ALDH1A1), an intracellular marker for ESCLCs, in ESCC cell lines and specimens.

Conclusions

CR-1 is a functional and cell surface ECSLC marker, and an independent prognostic indicator as well as a potential therapeutic target for ESCC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0650-7) contains supplementary material, which is available to authorized users.

Therapeutic strategies of drug repositioning targeting autophagy to induce cancer cell death: from pathophysiology to treatment

The 2016 Nobel Prize in Physiology or Medicine was awarded to the researcher that discovered autophagy, which is an evolutionally conserved catabolic process which degrades cytoplasmic constituents and organelles in the lysosome. Autophagy plays a crucial role in both normal tissue homeostasis and tumor development and is necessary for cancer cells to adapt efficiently to an unfavorable tumor microenvironment characterized by hypo-nutrient conditions. This protein degradation process leads to amino acid recycling, which provides sufficient amino acid substrates for cellular survival and proliferation. Autophagy is constitutively activated in cancer cells due to the deregulation of PI3K/Akt/mTOR signaling pathway, which enables them to adapt to hypo-nutrient microenvironment and exhibit the robust proliferation at the pre-metastatic niche. That is why just the activation of autophagy with mTOR inhibitor often fails in vain. In contrast, disturbance of autophagy–lysosome flux leads to endoplasmic reticulum (ER) stress and an unfolded protein response (UPR), which finally leads to increased apoptotic cell death in the tumor tissue. Accumulating evidence suggests that autophagy has a close relationship with programmed cell death, while uncontrolled autophagy itself often induces autophagic cell death in tumor cells. Autophagic cell death was originally defined as cell death accompanied by large-scale autophagic vacuolization of the cytoplasm. However, autophagy is a “double-edged sword” for cancer cells as it can either promote or suppress the survival and proliferation in the tumor microenvironment. Furthermore, several studies of drug re-positioning suggest that “conventional” agents used to treat diseases other than cancer can have antitumor therapeutic effects by activating/suppressing autophagy. Because of ever increasing failure rates and high cost associated with anticancer drug development, this therapeutic development strategy has attracted increasing attention because the safety profiles of these medicines are well known. Antimalarial agents such as artemisinin and disease-modifying antirheumatic drug (DMARD) are the typical examples of drug re-positioning which affect the autophagy regulation for the therapeutic use. This review article focuses on recent advances in some of the novel therapeutic strategies that target autophagy with a view to treating/preventing malignant neoplasms.